Synthesizing frontiers in modeling drought- and insect-induced tree mortality with climate change

Principal Investigator(s): 

William Anderegg, Jeffrey Hicke, and Rosie Fisher

Forest ecosystems cover approximately 30% of Earth’s land surface. They provide numerous ecological, economic, social, and aesthetic benefits across many spatial scales. At local scales, forests structure communities and regulate ecosystem processes and services. At global scales, forests serve as strong and persistent carbon sinks and exert substantial influence on carbon and water cycling, as well as climate regulation. Forests store 45% of carbon found in terrestrial ecosystems and may sequester as much as 25% of annual anthropogenic carbon emissions to the atmosphere.

Yet the sensitivity of forests to drought, temperature, and insect infestations has become apparent in global patterns of widespread forest mortality and increased rates of tree mortality. Drought and heat stress on forests is expected to intensify in many regions with climate change, but current climate-vegetation models rarely incorporate mortality due to drought or infestation, or the interactions between insects and trees. Thus, widespread tree die-off is a major unknown in predicting the impacts of climate change and ecosystem feedbacks to climate change.

This working group draws together a broad group of forest ecologists, physiologists, entomologists, and vegetation modelers to synthesize the state of knowledge on the relative role of drought and insects in major tree mortality events, including the interactions between drought tree stress and insect/disease population dynamics and attack rates. In addition, the group will summarize the modeling approaches of drought- and insect-caused tree mortality for simulating the impacts of future climate change on these disturbances and identify datasets that can be used as benchmarking tests for model validation and intercomparisons.

UPDATE October 2013

The Tree Mortality Group had two very productive meetings to chart a path forward for understanding and modeling tree mortality from insects and drought, as well as tree-insect interactions during drought. We have focused on synthesizing the key elements and uncertainties in tree drought physiology, insect populations and their climate sensitivities, and tree-insect interactions that would be important to incorporate into predictive models.


The Group anticipates submitting two review papers in the coming months. The first will focus on tree-insect interactions, providing a framework for how insect populations could be linked to tree physiology through tree defenses and other pathways. The second paper will focus on the synthesis of available mortality datasets that could be used to test and validate mortality algorithms in ecosystem models across multiple ecosystems. This paper is likely to include supplementary tables that provide links to these datasets and meta-data on coverage, availability, and other relevant fields.

More information about this project.

This work is supported by the National Center for Ecological Analysis and Synthesis, a Center funded by NSF (Grant #EF-0553768), the University of California, Santa Barbara, and the State of California.